1. Field of the Invention
This invention relates to processes and products of said processes. More specifically, this invention involves a high yield process for preparation of 2-anthryl and substituted 2-anthryl functional monomers. The monomers resulting from such processes can be polymerized to high molecular weight (M.sub.w .gtoreq.10.sup.4, degree of polymerization .about.40 or greater). These polymers readily form self-supporting films which are intrinsically photoconductive in the ultraviolet region of the electromagnetic spectrum.
2. Description of the Prior Art
The formation and development of images on the imaging layers of photoconductive materials by electrostatic means is well-known. The best known of the commercial processes, more commonly known as xerography, involves forming a latent electrostatic image on the imaging layer of an imaging member by first uniformly electrostatically charging the surface of the imaging layer in the dark and then exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered conductive and the electrostatic charge selectively dissipated in thse irradiated areas. After the photoconductor is exposed, the latent electrostatic image on this image bearing surface is rendered visible by development with a finely divided colored electroscopic material, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface which retain the electrostatic charge and thus form a visible powder image.
The developed image can then be read or permanently affixed to the photoconductor where the imaging layer is not to be reused. This latter practice is usually followed with respect to the binder type photoconductive films (e.g. zinc oxide pigment in a film forming insulating resin) where the photoconductive imaging layer is also an integral part of the finished copy. In so-called "plain paper" copying systems, the latent image can be developed on the imaging surface of a resuable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photoconductor, it is subsequently transferred to another substrate and subsequently permanently affixed thereto. Anyone of a variety of well-known techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with transparent films, and solvent or thermal fusion of the toner particles to this support of substrate.
In the above "plain paper" copying systems, the materials used in the photoconductive layer should preferably be capable of rapid switching from insulating to conductive to insulating state in order to permit cyclic use of the imaging layer. The increase in the rate of dark decay of the photoconductor. This phenomenon, commonly referred to in the art as "fatigue", has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of the materials suitable for use in such a rapidly cycling imaging system include anthracene, sulfur, selenium and mixtures thereof (U.S. Pat. No. 2,297,691); selenium being preferred because of its superior photosensitivity.
In the past, the use of anthracene in photoconductive insulating layers has been limited exclusively to the inclusion of the crystalline form of this material in a binder, since high molecular weight anthracene functional polymers have been virtually impossible to prepare. For example, attempts to synthesize high molecular weight anthracene polymers from 9-vinylanthracene by free radical initiated polymerization techniques generaly yields only oligomers. Attempts at cationic polymerization of these same monomers yields only low molecular weight materials of questionable structure; postulated to be a mixture of low molecular weight polymeric materials containing structural units from 9-vinylanthracene and 9,10-dimethyleneanthracene. Anionic polymerization of 9-vinylanthracene also yields only oligomers having a degree of polymerization in the range of from about 4 - 12. Attempts to copolymerize 9-vinylanthracene with other monomers, such as styrene, does not apparently improve the chances of obtaining polymeric products of high molecular weight. Apparently, resonance stabilization of the anthracene free radical under the conditions prevailing during such polymerization, favors formation of a non-propagating radical thus preventing the further growth of the polymer chain, A. Rembaum et al, Macromol Rev. 1, 57 (1967).
Apparent attempts at preparation of homopolymers of 2-vinylanthracene and 1-vinylanthracene and styrene copolymers thereof have proven equally fruitless, yielding only low molecular weight products.
Recently, the synthesis of copolymers of 9-anthrylethyl acrylate and methyl methacrylate has met with limited success; Vysokomolekulyarnye Soedineniya A14(5): 1127-31 (1972). The anthracene functionality of these copolymers (generally less than 11 %) provides luminescent markers (scintilators) for assistance in the study of the relaxation properties and conformation transformation of methyl methacrylate. Other copolymers containing anthracene groups have also been synthesized including polycondensates, formaldehyde resins, oligoarylenes; however, all of these polymeric products have relatively poor mechanical properties and cannot be readily formed into self-supporting films.
It is, therefore, the object of this invention to remove the above as well as related deficiencies in the prior art systems.
More specifically, it is the principle object of this invention to provide a process for preparation of anthracenic monomers in high yields.
Another object of this invention is to provide anthracenic monomers which can be readily polymerized into high moelcular weight anthracenic functional polymers.
Still another object of this invention is to provide a process for polymerization of such anthracenic monomers into anthracenic functional polymers.
Yet another object of this invention is to provide a high molecular weight scintilating polymer having anthracenic functionality.
It is a further object of this invention to provide an anthracenic functional polymer suitable for use in photoconductive imaging members and methods.